The NI values were calculated using R-scripts that use functions from the R-package NIcalc developed for the Norwegian NI. Much of this concerns estimating uncertainty of the NI. These scripts read data from the database and finds the appropriate statistical distribution for the uncertainty information for each indicator and uncertainty information for each Reference Value. The scripts then:
a) Draw random samples for each indicator
b) Scale the sampled values to the Reference Values using a defined scaling model (Fig.4) (c) Calculate weights based on the area
d) Calculate a sampled index value for a specified number of times (For e.g. 1000).
The median of these sampled index values can then be used as the NI value, and the 2.5th and 97.5th quantiles as a 95 percent confidence interval. However, if there is no information about the uncertainty of indicator values, no confidence interval for the NI can be calculated. If only some indicators have such information about uncertainty, the confidence interval for the NI will be biased. Since this was the case here, the NI values reported below were calculated as the mean of the scaled indicator values, without any confidence intervals (see also http://brage.bibsys.no/xmlui/bitstream/ handle/11250/2374610/3/1226.pdf)
The data of the indicator species were collected from various secondary sources and the Reference Value for the indicator species were determined with the help of experts. The indicators were scaled in such a way that they measure deviation from a Reference State, which is specified as an ecologically sustainable state for the indicator. NI is an average of the scaled values, and values range between 1 (Reference State) and 0 (very poor state). For calculating the NI value, the time series data were fed into the NI-India database and the NI values were calculated using R-scripts. The analysis of the indicator values were carried out with the help of NINA and the status of each indicator species is described in this section.
4.1. Chilika Lake
In Chilika Lake, data was available for all the indicators from the year 2000 to 2015, for every 5 year period (Fig.6) and exhibits the number of indicators used for calculating the NI value. The time series data of the indicator species were collected from various secondary sources from the year 2001 to 2015 and the year 2003 data was taken as a Reference Value against which all other year values were compared.
Note: This is a pragmatic solution and not generally recommended within the NI framework, because the year may not represent the same state for all parts of the ecosystem and it also may not represent a very good state.
In Chilika, the data for all the species were aggregated into 5-year periods using the mean of the available yearly data for each 5-year period. In the Island region, only the bird count was taken into consideration while calculating the NI value. Apart from that, data was available for all the indicator species in all sectors for every 5-year period.
4. Results
Figure 6: Number of indicators used to calculate Nature Index
Figure 7: NI value for 5-year period in Chilika Lake
4.1.1. Nature Index Value of Chilika Lake
Figure 7 indicates the fact that the overall NI value of the Chilika Lake (above 0.75) was good. This in turn indicates that the biodiversity status of the lake was good from the year 2000 to 2015. The highest value was recorded during the year 2005, which may be due to the restoration activities carried out from 2000 to 2003.
It was also reported by the ZSI that six species have reappeared after the restoration phase of the Chilika Lake.
The sectoral NI values calculated in all the 5 sectors (CS, Island, NS, OCS and SS) were compared with each other to understand the area wise deviation of the NI values. It was observed that the NI values of OCS and Island were good and varied between 0.75 to 1.00. The NI values of SS, CS and NS fluctuated (above 0.50 and below 0.75) during the year 2015 and there was a decline in the population after the year 2010 in all these sectors as indicated in Fig.8. The maximum NI was recorded in the OCS region, because this sector provides habitat for fresh water and brackish water species, and migratory routes for marine and freshwater species.
The Nalabana Island provides habitat for different types of migratory and resident bird species, and excellent breeding and feeding habitat for the birds to nourish, hence the NI value of the Island was good.
4.1.2. Thematic Index Value
The thematic Index exhibits the status of fish and bird population in Chilika Lake. In Chilika Lake, the maximum bird population was recorded in OCS, CS and Nalabana Island (NI value was above 0.8). Moderate values were recorded in SS (above 0.7) and NS (above 0.6) from 2010 to 2015 and there was a decline in bird population from the year 2005 onwards. For fish diversity, the OCS recorded the maximum value of above 0.8 during the year 2015. In the other sectors, the NI values fluctuated (SS >0.9 to <0.7; NS >0.7 to <0.6; CS >0.7 to <0.6) between 2000 to 2015 (Fig.9).
Figure 8: Nature Index value (5-year periods) for the five areas of Chilika Lake
Figure 9: Thematic NI value (5-year periods) for the five areas of Chilika Lake
Figure10: Map of Nature Index values for the five areas of Chilika
The status of NI can also be visualised through the colour coded maps depicted in Fig.10. The colour- coded map indicates the fact that the NI value is declining in the NS and it is also showing a declining trend in SS and CS (the colour changes from green to yellow). The contributory factors for the decline in the NI value may include:
a) By-catch of juveniles and usage of destructive fishing gears b) Illegal prawn Gheries
c) Blockage of Palur canal by barrier nets round the year
d) Dense growth of macrophytes, which causes deterioration of water quality e) Increased population of motorised boats
4.1.3. Fish
Figure 11: Observed and scaled value of Flat head mullet
1. Flat head mullet (Mugil ceplalus)
Flat head mullet is commonly called as Khainga and it is one of the high-value commercially important herbivore fishes found in brackish water. It is a demersal (inhabits the bottom area of the water body) catadromous species which migrates to the sea for breeding during September to January. It grows to a maximum size of 712 mm and forms more than 3% in the commercial catch. It has iliophagus feeding habits and mainly feeds on slime algae and detritus. The NI value of Flat head mullet was maximum and above the Reference Value range in OCS. In SC, the NI value was above the Reference Value until 2010 and the value slightly declined to
<0.75 (2010 to 2015). In NS and CS there was a moderate decline in the mullet population from the year 2005 to 2015. The reason for the depletion of the mullet population may be due to brood stock capture during seaward migration, destructive fishing practices and bycatch by the local fishing community (Fig.11). The IUCN red list status for this fish is Least Concern (LC).
Figure 12: Observed and scaled value of large scale mullet
3. Sea bass or Barramundi (Lates calcarifer)
The decrease in Sea bass population in NS may be due to the fluctuation of salinity, overfishing of brood stock and decrease in forage species. During the summer season, the brooders congregate near Muggermukh and migrate to the sea mouth region for spawning.
2. Large scale mullet (Liza macrolepis)
Large scale mullet is an ecologically significant herbivorous or detrivorous, demersal fish, which feeds on detritus. It remains in the lake from juvenile to adulthood stages for feeding. After that it migrates to the sea for spawning.
This is one of the highly prized or high-value fishes of mullet
group, which grows to a maximum size of 480 mm and contributes 0.8% of the commercial catch. It shows catadromous breeding behaviour, basically found in brackish water habitats and mainly feeds on detritus and algae (iliophagus feeding habits). It is a high-fecund brackish water fish. The large scale mullet population was maximum in OCS and SS (above the Reference Value). It was reported that there was a decline in the NI value of large scale mullet in the CS and NS, which may be due to the overexploitation of fishery resources by the local communities (Fig.12). The IUCN red list status for this fish is Least Concern (LC).
Figure 13: Observed and scaled value of Sea bass
4. Bengal corvina (Daysciaena albida)
Bengal corvina (Borogo) is a brackish water fish that breeds in lakes (Northern sector) and feeds on small fishes, prawns, amphipods, isopods and stomatopods. It contributes 6% of the commercial catch and grows to a very large size of 800 mm in Chilika.
It is a high-value fish species, which contributes nearly 5% of the commercial catch and helps in maintaining the balance in the food chain. It was noticed that there was a drastic reduction in the population in the CS and SS regions from the year 2000 onwards. A minimum value of <0.25 was recorded in SS and CS (>0.25) during 2015 (Fig.14). This may be due to overfishing, particularly juveniles and decrease in spawning stock biomass (SSB) in CS and SS.
Sea bass (Bhekti) is a demersal, catadromous and carnivore species. It lives both in marine and brackish water ecosystems and grows to large sizes (23 kg recorded in Chilika). It is a high-value fish, which contributes more than 1% in commercial catch. It breeds in the coastal water during June and July. The juvenile enters into estuaries, lagoons and brackish water for feeding and during summer the brooders congregate near Muggermukh and migrate to the sea mouth region for spawning. It feeds mostly on small fishes and prawn (more than 90%). Bhekti exhibits protandrous hermaphrodite characteristics. The mature Bhekti functions as male for one or more spawning seasons before it undergoes sex reversal. The NI value was recorded maximum in OCS, SS (above the Reference value) and CS regions (above 0.75) and showed a good population trend during the study period. There was a decline in NS where a minimum value of <0.25 was recorded during 2010 and a slight increase was noticed (>0.25) during the year 2015 (Fig.13).
Figure 14: Observed and scaled value of Bengal corvine
Figure 15: Observed and scaled value of four finger threadfin
5. Fourfinger Threadfin (Eleutheronema tetradactylum)
Fourfinger threadfin fish (Sahala) is a high-value threadfin species, which contributes more than 2.7% of the commercial catch. It breeds in the sea and lake, performing inter sea-lake movements. It grows to a large size of 1000 mm in the lake. It is amphidromous, neritic (lives in shallow part of the ocean) and largely feeds on prawns, fish and plankton. There are indications of recruitment twice a year (February to April and August to
September) and it breeds both inside the sea as well as in the lake and prefers sea-lake movement. This species is susceptible for easy capture during their breeding seasons. In the OCS region, the NI value was above the Reference Value. In NS and SS, the NI value was moderate (above 0.50). In CS the value declined from 1.0 to below 0.50 between 2010 to 2015 (Fig.15). The decrease in value may be due to bycatch and overexploitation.
Figure 16: Observed and scaled value of Pearl spot
6. Pearl spot (Etroplus suratensis)
Pearl Spot (Kundala) is an indigenous brackish benthopelagic fish found in peninsular India. It is a high-value resident cichlid species in the lake, which breeds in the lake throughout the year (two peak periods are: December-February and April-May). The fish starts maturing to a length of above 105 mm
and grows to the maximum size of 305 mm in the lake. This is an important aquaculture species cultured both in brackish and fresh water. This species is commercially important and contributes more than 1% of the total landing in Chilka. Pearl spot is an herbivorous species, which feeds on weeds (48%), algae (12%), detritus (34%), gastropods (4%) and other miscellaneous matters (2%).
It was recorded that the pearl spot population was above the Reference Value in CS and SS, from the year 2000 to 2015. In NS and OCS, there was a decline in the NI value from the year 2000 to 2010 but the value gradually increased to a maximum of 1.0 during the year 2015 (Fig.16). Pearl spot showed a healthy population status in all the four sectors, as it can survive and grow well in both fresh water and brackishwater. The IUCN red list status for this fish is Least Concern (LC).
7. Hilsa shad (Tenualosa ilisha)
Hilsa shad (Ilishi) is an anadromous fish which occurs mostly in NS (freshwater zone). It emigrates from the sea to the lake mainly for breeding in the freshwater zone during monsoon months and emigrates during winter for feeding. It is a high-value fish, which currently exhibits a declining trend forming
an average of 0.5% of composition of the commercial landing. It grows to a maximum size of 515 mm in the lake. The annual landing has declined in the lake most likely due to habitat damage by weed infestation in the river mouth zone, siltation at the spawning ground and deeper migratory channel in the northern sector, intensive destructive fishing activities in the outer channel sector and overfishing. It is also observed that there is a marked decline in the coastal population of the fish which may have caused the decline of Hilsa fishes in the lake.
Hilsa population was above the Reference Value in the NS, but there was a drastic decline in population in all the other sectors (CS, OCS and SS) from the year 2005 onwards. The scaled value may not reflect the actual status in this sector, because of the low Reference value. All these sectors have reached the minimum NI value of 0.25 during the year 2015, due to over exploitation by the local fishers. The brood stocks are captured in seine nets and a high mortality rate of 70-84% was recorded in these sectors (Fig.17). The decline in the population and catch of this very important commercial fish species is a serious concern. The IUCN red list status for this fish is Least Concern (LC).
Figure 17: Observed and scaled value of Hilsa shad
8. Grey eel-catfish (Plotosus canius)
Grey eel-catfish (Kaunda) is a resident species in Chilika, which is dominantly available in the northern and central sectors of the lake. It breeds in the bottom muddy substratum. It is primarily a carnivore, which feeds largely on shrimps, molluscs, and so on.
9. Spot tail needle fish (Strongylura strongylura)
Spot tail needle fish (Gania) is considered as a resident species in Chilika, which breeds in the lake throughout the year. It is a high-value fish forming about 2.5% of the commercial catch and it feeds on small clupeoid fishes. It
The Grey eel grows to a maximum size of 1060 mm. NS is the favourite breeding site for this species due to the availability of soft mud bed. Mostly it breeds during May to September, July being the peak month. The efficient fishing gear of the species is hook and line, therefore the population density is well maintained. The NI value of the Grey eel was good in all the sectors from the year 2000 to 2015 (Fig.18).
is a pelagic neritic fish and the juvenile of this species emigrate from the marine waters to the fresh water and completes its life cycle in Chilika Lake. It is also one of the commercially important finfish species, which fetches lucrative prices for the local fishermen.
Figure 18: Observed and scaled value Grey eel catfish
Spot tail needle fish breeds in CS at Nalabana and also in NS area near Tuanali during June and July. The population status of the needle fish was good until 2010 in all the sectors. There was a decline in the population from the year 2010 to 2015, when a minimum value of <0.25 was recorded in NS. In SS and CS, the NI value was above 0.25 (Fig.19). The decreasing trend is noticed due to the increase in market demand, hence overfishing is prevalent by the local fishing communities.
Figure 19: Observed and scaled value of Spot tail needle fish
10. Bloch gizzard shad (Nem atalosa nasus)
Bloch’s gizzard shad (Balangi) is a brackish, freshwater pelagic-neritic and anadromous clupeoid fish. It is a commercially viable species in Chilika with an average annual landing of 943 tonnes, contributing to nearly 8% of
the commercial catch. Balangi enters from the marine water and completes its life cycle in Chilika lake. The matured marine stock immigrates into the lake for breeding from January to June and prefers sandy areas for breeding.
The mean length of the species varies between 135-175 mm and it feeds on decayed organic matter or detritus and large amounts of benthic foraminifera along with mud (65%). The NI value was good in OCS, SS (above the Reference Value) and NS (>0.50 in the year 2015) and there was a decline in the Bloch’s gizzard shad population in CS from the year 2005 onwards and it reached a minimum value of <0.50 during the year 2015 (Fig.20). The IUCN red list status for this fish is Least Concern (LC).
Figure 20: Observed and scaled value of Bloch’s gizzard shad
11. Small Bengal Silver-biddy (Gerres setifer)
The small Bengal silver-biddy (Jagili) live both in the marine and brackish water regions. It is a benthopelagic, amphidromous fish that has a high commercial value and contributes 1.1% (approximately 129 tonnes) of the total
catch. The peak breeding season of Jagili is June and it breeds mostly in the sandy bottom area. The fish feeds on crustaceans (42%), molluscs (31%), algae (6%), decayed organic matter (13%) and miscellaneous matter (8%). The overall mean length of the fish is 110 mm. The population status of Small Bengal Silver-biddy was above the Reference Value in the CS and SS regions from 2000 to 2015. In OCS, there was a decline in the population (<0.50) during 2010 and it gradually increased to the maximum index value of 0.1. In NS, the value was constantly low from the year 2000 onwards (<0.25) and showed a very poor population density, which may be due to overfishing in the freshwater region by the local community (Fig.21).
Figure 21: observed and scaled value of small Bengal silver
12. Long Whiskers Catfish (Kantia) (Mystus gulio)
Long whiskers catfish (Kantia) live both in brackish as well as fresh water. It is an anadromous fish endemic to Chilika lake and one of the high-value commercial fish being caught in the lake throughout the year. It grows to a size of 131 mm.
The average annual landing was 594.22 tonnes (4.98%) and its favourable habitat is mud and clay substrates.
It feeds on amphipods (31%), prawns (13%), algae (13%), detritus (8%), higher plant matter (5%), fish (5%), mysids (4%), gastropods (4%), isopods (3%), insects (2%) and miscellaneous (12%). This catfish completes its life cycle within the lake and breeds from June to November, August being the peak breeding period. The Nalabana bird sanctuary situated in the CS is known to be the important spawning ground of this species.
Maximum NI values (above the Reference Value) were recorded in OCS and SS regions. There was a decline in catfish population in CS and NS from the year 2005 onwards and it recorded a minimum value of <0.50 in CS and <0.25 in NS during the year 2015 (Fig.22). The IUCN red list status for this fish is Least Concern (LC).
Figure 22: Observed and scaled value of Long whiskers catfish
13. Goldlined sea bream (Rhabdosargus sarba)
Goldlined seabream (Rhabdosargus sarba, locally called as Dhala Khuranta) lives both in brackish and sea water regions. The juveniles emigrate from the sea to Chilika Lake and it remains in the lake for feeding and growing until it attains adulthood.
The average annual landing is estimated as 164.35 tonnes and contributes 1.38% of the total catch in Chilika.
It feeds on algae (31%), molluscs (20%), crustaceans (17%), organic detritus (12%), larger aquatic plants (11%) and miscellaneous matter (11%). The mature adults congregate at the lake mouth near OCS just before spawning and migrates to the sea for spawning. The NI value was high in the OCS (above the Reference Value) and CS (>0.75) regions. In OCS, it has drastically increased from 0.25 to 1.0 from the year 2000 to 2015, which may be due to increase of inward migration of spawning population. The NI value was moderate in NS (0.50)
It feeds on algae (31%), molluscs (20%), crustaceans (17%), organic detritus (12%), larger aquatic plants (11%) and miscellaneous matter (11%). The mature adults congregate at the lake mouth near OCS just before spawning and migrates to the sea for spawning. The NI value was high in the OCS (above the Reference Value) and CS (>0.75) regions. In OCS, it has drastically increased from 0.25 to 1.0 from the year 2000 to 2015, which may be due to increase of inward migration of spawning population. The NI value was moderate in NS (0.50)